1. Field of the Invention
The present invention relates to a multiple disc clutch device disposed between the engine and the transmission of, for example, a motorcycle and adapted to make and break a power transmitting connection thereby to selectively transmit the power of the engine to the transmission.
2. Description of the Prior Art
A typical known multiple disc clutch device of the kind mentioned above is constituted mainly by the following parts: namely, a cylindrical clutch outer member opened at its one end surface and closed at the its other end surface; a plurality of driving clutch discs each having a plurality of engaging convex portions formed on an outer peripheral surface thereof, the engaging convex portions being in engagement with engaging concave grooves formed in an inner peripheral surface of the cylindrical portion of the clutch outer member along the generating lines of the latter at a constant circumferential pitch; a driven gear provided on the outer surface of the closing end of the clutch outer member; and a buffer spring interposed between a first spring retainer formed on the driven gear and a second spring retainer formed on the closing end surface of the clutch outer so as oppose to the first spring retainer.
There are two ways for increasing the capacity of the clutch device of the kind mentioned above. The first way is to increase the number of the clutch discs, while the second way is to increase the set load of the clutch spring. Usually, the second way is preferred particularly when the desired clutch capacity exceeds a certain level, because the adoption of the first way is restricted by an accompanying requirement for a greater manipulation force on the clutch lever.
Hitherto, the annular core of the driving clutch disc is formed by die-casting from an aluminum alloy to have a considerably large thickness, so that an increase of the number in the clutch discs to be disposed therein inconveniently requires increasing the axial length of the apparatus resulting in a greater size of the clutch device as a whole. It is possible to reduce the axial length of the clutch device by forming the annular core metal of the driving clutch disc from a steel sheet having a smaller thickness. This, however, imposes a new problem. Namely, since the clutch outer member is formed of an aluminum alloy by die-casting, the engaging concave grooves formed therein are rapidly worn due to a large surface pressure exerted thereon by the annular core metal. This problem will be overcome by employing a greater number of engaging concave grooves, but the increase in the number of the engaging concave grooves is naturally limited for reasons concerning the formability and strength inherent to a die-cast clutch outer member.
The clutch outer member made of aluminum alloy suffers from another problem: that its second spring retainer, which is always in sliding contact with the buffer spring, is worn rapidly due to repeated contraction and extension of the buffer spring. In some cases, in order to obviate this problem, a steel seat is mounted on the second spring retainer. This countermeasure, however, is not desirable because not only the number of parts but also the number of steps of the assembling process is increased due to the necessity for positioning of the steel seat.